Free PSA Test

PSA is a protein made by the prostate. Most of it travels through the blood bound to other proteins; a smaller share circulates free. A standard PSA test measures both together - your total PSA. A free PSA test measures only the unbound portion, and the lab then calculates the free‑to‑total ratio, usually reported as a percentage (% free PSA). The reason this matters: prostate cancer tends to produce PSA that binds readily to blood proteins, while benign prostatic hyperplasia (an enlarged prostate, very common after 50) tends to release more free PSA. Two men can have the same total PSA of 4.5 µg/L for entirely different reasons, and the ratio is one of the things that helps separate them. It is most informative when total PSA is mildly raised rather than clearly normal or clearly high. If your total PSA is well below the action threshold for your age, the ratio adds little. If it is substantially elevated, you need a doctor and imaging, not another blood marker.